Generally, as opposed to disposable primary batteries, secondary batteries refer to rechargeable batteries, and are being widely used for electronic devices such as mobile phones, laptop computers and camcorders, or electric vehicles. Particularly, lithium secondary batteries are a fast growing trend in many industries due to having a higher capacity than nickel-cadmium batteries or nickel-hydrogen batteries widely used for a power source of electronic devices and high energy density per unit weight.
A lithium secondary battery uses lithium-based oxide and a carbon material for a positive electrode active material and a negative electrode active material, respectively. The lithium secondary battery has an electrode assembly including a positive electrode plate and a negative electrode plate respectively coated with the positive electrode active material and the negative electrode active material with a separator interposed therebetween, and a packaging, namely, a battery case, in which the electrode assembly is received together with an electrolyte solution in an airtight manner.
Lithium secondary batteries can be classified into can-type secondary batteries in which an electrode assembly is received in a metal can and pouch-type secondary batteries in which an electrode assembly is received in a pouch of an aluminum laminate sheet, according to the shape of the packaging. These secondary batteries are generally fabricated through a process in which an electrolyte solution is injected into a packaging where an electrode assembly is received, and the packaging is sealed.
On the other hand, because medium and large-sized battery packs are preferably manufactured to be as small and light as possible, prismatic batteries and pouch-type secondary batteries wherein stacking can be used to achieve integration and high capacity relative to weight can be obtained are mainly used for battery cells of medium and large-sized battery packs. Particularly, preference of pouch-type secondary batteries is high in recent years. Because pouch-type secondary batteries have light weight, have the low likelihood of electrolyte solution leakage, and is flexible in shape, their advantage is that secondary batteries having the same capacity can be realized with lower volume and mass.
A pouch-type secondary battery includes a pouch case and an electrode assembly as a basic structure. The electrode assembly has a structure in which a unit cell including a negative electrode plate, a separator, and a positive electrode plate is stacked in a repeated manner. Each unit cell has a positive electrode tab and a negative electrode tab, and the positive electrode tabs and the negative electrode tabs converge in a predetermined direction and are respectively joined to a positive electrode lead and a negative electrode lead having an attached insulation tape by a method such as resistance welding, ultrasonic welding, and laser welding. The electrode lead performs a function of electrically connecting the secondary battery to an external device.
The secondary battery is fabricated through a process of placing the electrode assembly in an internal space defined by the pouch case, a process of sealing the periphery of the pouch case except an electrolyte solution injection part by heat fusion, a process of injecting an electrolyte solution through the electrolyte solution injection part, a process of applying heat fusion to the electrolyte solution injection part to completely seal the pouch case, a process of tailoring an unnecessary residual portion of the electrolyte solution injection part, a process of aging the secondary battery, and a post-treatment process such as initial charging and testing.
The pouch-type secondary battery has an empty space between the pouch case and the electrode assembly according to the structural characteristics. Therefore, if the pouch-type secondary battery is placed in a situation such as vibration or collision, the electrode may poke out toward the empty space in the pouch case and come into contact with the tab portion, causing a short and a fire. Accordingly, there is a need for an approach to enhance the safety by solving the problem of the pouch-type secondary battery such as an internal short.